Apparatus for presenting a sample of material for analysis

ABSTRACT

An apparatus for presenting a sample of material for analysis by a laser-based analyzer comprises a chamber, a first window for admitting laser radiation to the chamber, sample presentation means for presenting a sample such that said laser radiation can impinge upon the sample, and a plurality of second windows ( 76,78,80,82 ) for receiving radiation emitted from the sample, said plurality of second windows ( 76,78, 80,82 ) adapted to pass radiation emitted from the sample to a plurality of detector means. The apparatus further includes a gas inlet ( 98 ) and a gas outlet ( 100 ) to enable the atmosphere inside the chamber ( 52 ) to be controlled.

FIELD OF THE INVENTION

The present invention relates to an apparatus for presenting a sample ofmaterial for analysis. The apparatus is especially suitable forpresenting a sample of material for analysis by a laser-based analyser.

BACKGROUND OF THE INVENTION

International patent application no. PCT/AU99/00713 in the name of thepresent applicants describes a laser-based analyser. This analyser canbe used to analyse solid, liquid or even gaseous materials. However, theanalyser is most suitably used for analysing solid materials, such ascoal.

In the analyser described in international patent application no.PCT/AU99/00713, laser radiation is focussed onto a sample, which causesthe sample to emit light. The emitted light is detected by a pluralityof detectors. The plurality of detectors detects information fromspecific parts of the spectral region and forwards that information torespective data collecting means.

An embodiment of the analyser described in international patentapplication no PCT/AU99/00713 is described with reference to FIG. 1attached hereto.

In the apparatus shown in FIG. 1, a laser 10, which may be a 1064 mmND:YAG laser, emits pulses of laser light that are focussed by anoptical system 12 onto a material to be analysed 14. In the small regionof the laser spot focused on the material 14, the laser power densityproduces rapid heating and ionisation of a small sample of the material.Light is emitted from the vaporised and ionised material containingspectral information on the material involved. The light emitted fromthe vaporised and ionised material is schematically represented at 16and this emitted light is detected by a plurality of detection means 20,22, 24. The apparatus shown in FIG. 1 has three detection means but itwill be appreciated that a lesser or greater number of detection meansmay be utilised. It is envisaged that a greater number of detectionmeans may be utilised if especially high resolution is required.Detection means 20 comprises a spectrometer 26 that is adjusted to apart of the spectrum of the spectral emissions emanating from material14. Detection means 20 also includes a CCD detector 21 which suitablycomprises a readily available commercial CCD detector. The CCD detector21 may comprise a 12–16-bit detector.

Similarly, detection means 22 comprises a spectrometer 30 and a CCDdetector 32. Detection means 24 also comprises a spectrometer 34 and CCDdetector 36.

The CCD detectors 21, 32, 36 detect information from the specificspectral region provided by their associated spectrometers. The CCDdetectors then pass the detected information to respective dedicateddata acquisition means 38, 40, 42. The data acquisition means mayinclude analog-to-digital conversion boards/circuitry. The computer 44also includes control means 46 to control the operation of the laser 10and the plurality of the detection means 20, 22, 24.

In use of the apparatus shown in FIG. 1, the control means 46 sends acontrol signal to laser 10 which causes the laser to emit a pulse oflaser light. The pulse of laser light 10 is focused onto the surface ofmaterial 14 which causes vaporisation and ionisation of a small part ofthe material 14.

Shortly after the control signal causes a pulse of laser light 10 to beemitted by the laser, the control means 46 sends control signals to thedetection means 20, 22, 24 which turns on those detection means. It ispreferred that there is a slight delay between firing of the laser andinitialisation of operation of the spectrometers in order to ensure thatthe CCD detectors do not detect the pulse of laser light and only detectthe emitted spectra. This control signal causes the spectrometers 26,30, 34 to collect light from the relevant spectral region for apredetermined period of time and to enable the CCD detectors 21, 32, 36to detect that light. Each of spectrometers 26, 30, 34 collect lightfrom particular regions of the emission spectrum. The particular regionsmay be discrete, separate regions of the spectrum, or there may be someoverlap between the spectral region collected by one of thespectrometers and the spectral region collected by another of thespectrometers. Whilst the detection means 20, 22, 24 are collecting anddetecting the light from the emitted spectral region from the sample 14,the CCD detectors are also forwarding information to the respective dataacquisition means 38, 40, 42. The CCD detectors are formed fromindividual areas of light sensitive material (usually silicon) known aspixels. Each pixel converts the light intensity to an electric change orcurrent which is then digitised by the data acquisition means. The useof separate data acquisition means for each detection means enablesrapid collection of large amounts of data and this in turn allows therapid analysis of the material to take place at high spectralresolution.

The data collected by the data acquisition means 38, 40, 42 is thenanalysed by the computer to determine the elements of species present inthe material and also to determine the relative amounts of each of thoseelements or species. The amount of each element or species in thematerial may be determined by integrating the area under the spectralline at a wavelength that is characteristic of the spectral emission ofa given element or species and comparing that area with the area underthe same spectral line obtained from a material having a known contentof that particular element or species.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus forpresenting a sample of material for analysis.

In the first embodiment, the present invention provides an apparatus forpresenting a sample of material for analysis by a laser-based analysercomprising a chamber, a first window for admitting laser radiation tothe chamber, sample presentation means for presenting a sample such thatsaid laser radiation can impinge upon the sample, and a plurality ofsecond windows for receiving radiation emitted from the sample, saidplurality of second windows adapted to pass radiation emitted from thesample to a plurality of detector means.

In one embodiment, the chamber has one or more walls to define aninterior thereof. The first window and the plurality of second windowsare preferably formed in the walls of the chamber.

Preferably, the sample presentation means presents the sample to theinterior of the chamber.

The sample presentation means is preferably removably secured to one ormore walls of the chamber. More preferably, a wall of the chamber has anaperture therein and the sample presentation means positions the sampleover, in or through, the aperture such that laser radiation can passthrough the first window and impinge upon the sample.

It is especially preferred that the sample presentation means forms agas-tight seal when the sample presentation means is secured to the wallof the chamber. The gas-tight seal may be achieved, for example, byproviding a sealing gasket on the outside of the wall to which thesample presentation means is removably secured.

In one embodiment, the first window comprises or includes a lens toenable laser radiation to be focussed onto the sample. The position ofthe lens may suitably be adjustable to allow the focussing point for thelaser radiation to be adjusted. The lens is suitably placed in anadjustable mount to allow focussing onto the surface of the sample beinganalysed. This is a useful feature that enables a number of separatesamples to be sequentially analysed by the analyser without requiringexact placement of each sample onto an identical location on the samplepresentation means.

Alternatively, and more preferably, the sample presentation means ismoved during irradiation of the sample by the laser so that the sampleis scanned across the laser beam. This assists in reducing any analysiserrors associated with sample heterogeneity.

It is also preferred that the plurality of second windows include orcomprise lenses for collecting and focusing emitted light from thesample. Similarly to the first lens, the plurality of second lenses mayalso be adjustable to enable their focal point to be adjusted.

The apparatus may further include laser holding means for holding alaser. Preferably, the laser holding means aligns an output of the laserwith the first window. Preferably, the laser holding means releasablyholds the laser.

In other embodiments, the laser holding means may be separate to theapparatus, such as a stand-alone stand.

The apparatus may also further comprise a plurality of detector holdingmeans for holding a plurality of detectors. The detector holding meanspreferably releasably hold the detectors. The detector holding meanspreferably align the detectors with respective second windows.

Preferably, the detector holding means align the detectors such that thedetectors detect emitted light from a position in front of the sample.Preferably, the detector holding means aligns the detectors such thatthe detectors detect emitted light from a position that is 1 to 5millimeters in front of the sample, more preferably about 2 millimetersin front of the sample.

In another embodiment, the second windows comprise or include lenses andthe lenses are focused to receive emitted light from a position in frontof the sample. Preferably the lenses in or part of the second windowsare focussed to receive emitted light from a position that is 1 to 5millimeters in front of the sample, more preferably about 2 millimetersin front of the sample.

The apparatus may further comprise atmosphere control means forcontrolling the atmosphere inside the chamber. The atmosphere controlmeans may comprise a gas inlet into the chamber for admitting gas intothe chamber and a gas outlet from the chamber for removing gas from thechamber. This enables a purge or a buffer gas to flow into the chamber.Alternatively, the chamber may have a vacuum port for applying a vacuumto the chamber. It will be appreciated that, in embodiments where theapparatus includes a gas inlet and a gas outlet, that a vacuum line maybe attached to either the gas inlet or the gas outlet if it is designedto apply a vacuum to the chamber.

The apparatus may further comprise dust collection means for collectingdust from the sample. The dust collection means is preferably removable.The dust collection means may suitably comprise a sliding tray.Preferably, the dust collection means is in sealing engagement with thechamber when the dust collection means is in a closed position. The dustcollection means most suitably is positioned in a lower part of thechamber.

In a further preferred embodiment, the apparatus comprises safetyinterlock means for preventing firing of the laser if part of theapparatus is open. In one embodiment, the safety interlock meanscomprises an interlock associated with the sample presentation means toprevent firing of the laser if the sample presentation means is notclosed. In another embodiment, the safety interlock means comprises aninterlock associated with the dust collection means to prevent firing ofthe laser when the dust collection means is not fully closed. Theinterlock means preferably comprises electrical interlock means.

In another embodiment, the plurality of second windows enable opticalfibres to receive emitted light from the sample. In this embodiment, theapparatus may also include optical fibre holding means for holding theoptical fibres in a desired position. In this embodiment, the opticalfibres are used to image the light emission from the sample.

When using optic fibre to transmit the emitted light observed throughthe plurality of second windows, the aperture of the fibre restricts theviewing zone to the region of maximum light emission (about 2 mm infront of the sample, typically). This is a convenient way of ensuringonly the light emission of interest is passed onto the spectrometers,thus resulting in superior signal-to-noise ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of the analyser described in thepresent applicant's international patent application no. PCT/AU99/00713;

FIG. 2 shows a schematic side view, in cross section, of an apparatusfor presenting a sample of material for analysis in accordance with thepresent invention;

FIG. 3 is a schematic diagram of the emission zone of light emitted fromthe sample and the focal area of the detectors;

FIG. 4 is a perspective view of the apparatus of FIG. 2;

FIG. 5 is a perspective view of an apparatus in accordance with thepresent invention showing optical fibres connected thereto; and

FIG. 6 is an end view of the apparatus of FIG. 5 with the sample holdingmeans removed therefrom.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It will be appreciated that the drawings shown in FIGS. 2 to 6 show apreferred embodiment of the present invention and have been provided inorder to illustrate that preferred embodiment of the invention. It is tobe understood that the invention should not be considered to be limitedto the embodiments as shown in FIGS. 2 to 6.

The apparatus shown in FIGS. 2 to 4 in accordance with the presentinvention is designed to be placed in the analyser in the region denotedby letter A in FIG. 1.

The apparatus 50 in accordance with the present invention and shown inFIG. 2 includes a chamber 52. The apparatus includes side walls 54, 56and an upper end wall 58. A sliding dust tray 60 seals what wouldotherwise be an open bottom of chamber 52.

As it can be seen from FIG. 2, side wall 54 has an aperture 62 therein.Sample presentation means, in the form of a sliding sample holder 64, isadapted to be removably secured to side wall 54. When sliding sampleholder 64 is in the position as shown in FIG. 2, aperture 62 in sidewall 54 is effectively closed by the sliding sample holder 64. A seal isachieved between the sliding sample holder 64 and the side wall 54 byuse of a gasket seal 66.

The sliding sample holder 64 is preferably machined out of a singlepiece of metal so that when the tray enters the side a round the end ofthe tray maintains the gas-tight integrity of the chamber.

Although the sample holder of FIG. 2 is shown as a sliding sampleholder, it will be appreciated that any other form of sample holder thatmay be releasably secured to the apparatus may also be used inaccordance with the present invention.

The sliding sample holder 64 includes a recess 68. Recess 68 receivesand holds a sample 70 in place. The sample 70 may, for example, comprisea coal sample. It is preferred that the surface of sample 70 isrelatively smooth.

The apparatus shown in FIG. 1 also includes a first window 72. Firstwindow 72 includes a lens. The lens position is adjustable to allowfocusing of the laser beam onto the sample.

The laser used in conjunction with the apparatus 50 shown in the Figuresis mounted in a separate laser holding means.

The apparatus 50 also includes a laser beam enclosing means 74 forguiding the laser beam from the laser into window 72. Laser beam guidingmeans 74 encloses the laser beam for safety purposes. The laser beamenclosing means 74 is best shown in FIG. 4. The laser beam enclosingmeans may suitably comprise a short tube having a set screw for securingthe end of the laser in position.

One or more mirrors may also be used to direct the laser beam into theassembly.

The apparatus also includes a plurality of second windows 76, 78, 80,82. Each of the second windows 76, 78, 80, 82 has a detector holdingmeans 84, 86, 88, 90 associated therewith for holding detectors fordetecting light emitted by the sample following a radiation of thesample with laser radiation. The detector holding means 84, 86, 88, 90most clearly shown in FIG. 4. As with laser holding means 74, thedetector holding means may comprise a short tube having a set screw forholding the detector therein. Other suitable arrangements for holdingthe detectors may also be used. A suitable detector may be an imaginglens and fibre optic conduit that transfers the emission to dector means20, 22 and 24.

The plurality of second windows 76, 78, 80, 82 are most preferablyformed as lenses to enable the light emitted by the sample to befocussed onto the detectors. Most suitably, the windows are formed bymachining or casting holes into the assembly that perfectly align withthe light emission from the sample and placing a lens in or over thehole.

It is also preferred that the plurality of fluorescence imaging devicesor detectors (such as lens assemblies) are positioned within andreleasably held by the detector holding means 84, 86, 88, 90 such thatthey are all exactly aligned to a desired point in the field of emittedlight from the sample. Most preferably, the multiple fluorescenceimaging devices are all exactly aligned to a point approximately 1 mm to5 mm in front of the sample, most preferably about 2 mm in front of thesample. This is clearly shown in FIG. 3 where the incident laser beam 92impinges on the sample and causes a spark 94 of emitted light to beemitted by the sample. The detectors held by the plurality of thedetector holding means 84, 86, 88, 90 are all aligned and focussed suchthat they image the image region 96 that is typically positioned 1 mm to5 mm in front of the sample, most preferably about 2 mm in front of thesample. In this regard, it has been found by the present inventors thatmaximum fluorescence response is obtained by focussing the laser ontothe sample. However, it is preferred that the detectors for detectinglight emitted by the sample are aligned to image the emitted light froma point positioned in front of the samples because the present inventorshave found that the maximum emitted light signal is observed from apoint just in front of the sample. Furthermore, imagining from a pointin front of the sample reduces interfering background fluorescence andreduces noise, thereby maximising the performance of the analyser.

The apparatus 50 may further include gas inlet 98 and gas outlet 100. Asshown in FIG. 1, gas inlet 98 and gas outlet 100 are positioned in anupper wall 58 of the apparatus. Although FIG. 2 appears to show only asingle gas inlet or outlet, it will be appreciated that gas inlet 98 andgas outlet 100 in FIG. 2 are positioned such that they are in alignmentwith each other in side view. The gas inlet 98 and gas outlet 100 may beused for supplying buffer gas into and out of the chamber 50.Alternatively, a source of vacuum may be connected to one of the gasinlet 98 or gas outlet 100 (or to both thereof) if it is desired toapply a vacuum to the chamber.

As best shown in FIG. 4, the apparatus may also include a lateralextending flange 102 projecting from a bottom part of the apparatus.Laterally extending flange 102 may include holes 104, 106 that enablethe flange to be securely bolted or otherwise affixed to a surface ofthe analyser. This ensures that the apparatus 50 is securely held inplace on the analyser.

In FIG. 4, the gas inlet 98 and gas outlet 100 have been omitted for thesake of clarity.

FIGS. 5 and 6 show another embodiment of the present invention. Thesefeatures of FIGS. 5 and 6 that are essentially the same as the featuresof the embodiment shown in FIGS. 2–4 are denoted by the same referencenumeral with a prime (′) added. Those features need not be describedfurther. In FIGS. 5 and 6, windows 76′, 78′, 80′, 82′, have fibre opticholders 84′, 86′, 88′, 90′, associated therewith to hold optic fibres110, 112, 114, 116. The optic fibres transmit the emitted light gatheredthrough windows 76′, 78′, 80′, 82′ to respective detectors.

Also shown schematically in FIG. 6 is safety interlock 110′. Safetyinterlock may comprise a switch or sensor that is responsive to thesliding dust tray 60′. When the dust tray′ is in its fully closedposition, switch or sensor 110′ detects that the dust tray is fullyclosed. This disables an electrical interlock between switch or sensor110′ and the laser to thereby enable the laser to fire. When the dusttray 60′ is not in its fully closed position, the sensor or switch 60′detects that fact and enables the electrical interlock, which preventsthe laser from firing.

If desired, a similar safety interlock can be fitted to prevent thelaser firing if the sliding sample holder 64 or 64′ is not fully closed.

Those skilled in the art will appreciate that the present invention maybe susceptible to variations and modifications other than thosespecifically described, it will be appreciated that the presentinvention extends to encompass all such variations and modificationsthat fall within its spirit and scope.

1. An apparatus for presenting a sample of material for analysis by alaser-based analyser comprising a chamber, a first window for admittinglaser radiation to the chamber, sample presentation means for presentinga sample such that said laser radiation can impinge upon the sample, anda plurality of second windows for receiving radiation emitted from thesample, said plurality of second windows adapted to pass radiationemitted from the sample to a plurality of detector means.
 2. Apparatusas claimed in claim 1 wherein the chamber has one or more walls todefine an interior thereof and said first window and said plurality ofsecond windows are formed in said one or more walls.
 3. Apparatus asclaimed in claim 2 wherein the sample presentation means is removablysecured to one or more walls of the chamber.
 4. Apparatus as claimed inclaim 3 wherein a wall of the chamber has an aperture therein and thesample presentation means positions the sample over, in or through theaperture such that laser radiation can pass through the first window andimpinge upon the sample.
 5. Apparatus as claimed in claim 4 wherein thesample presentation means forms a gas-tight seal when the samplepresentation means is secured to the wall of the chamber.
 6. Apparatusas claimed in any one of the preceding claims 1–2 wherein the firstwindow includes a lens to enable laser radiation to be focussed onto thesample.
 7. Apparatus as claimed in claim 6 wherein the position of thelens is adjustable to enable the focussing point for the laser radiationto be adjusted.
 8. Apparatus as claimed in claim 7 wherein the lens isplaced in an adjustable mount to enable focussing of the laserradiation.
 9. Apparatus as claimed in any one of claims 1 to 2 whereinthe sample presentation means is movable to allow the sample to bescanned across the laser beam during irradiation.
 10. Apparatus asclaimed in any one the preceding claims 1–2 wherein the plurality ofsecond windows include lenses for collecting and focussing emitted lightfrom the sample.
 11. Apparatus as claimed in claim 10 wherein theplurality of second lenses are adjustable to enable their focal point tobe adjusted.
 12. Apparatus as claimed in claim 10 wherein the lensescollect light from a position that is from 1 mm to 5 mm in front of thesample.
 13. Apparatus as claimed in any one of the preceding claims 1–2further comprising a plurality of detector holding means for holding aplurality of detectors.
 14. Apparatus as claimed in claim 13 wherein thedetector holding means align the detectors such that the detectorsdetect emitted light from a position that is from 1 mm to 5 mm in frontof the sample.
 15. Apparatus as claimed in any one of the precedingclaims 1–2 further comprising atmosphere control means for controllingthe atmosphere inside the chamber.
 16. Apparatus as claimed in claim 15wherein the atmosphere control means comprises a gas inlet into thechamber to admitting gas into the chamber and a gas outlet from thechamber for removing gas from the chamber.
 17. Apparatus as claimed inclaim 15 wherein the atmosphere control means comprises a vacuum portfor applying a vacuum to the chamber.
 18. Apparatus as claimed in anyone of the preceding claims 1–2 further comprising dust collection meansfor collecting dust from the sample.
 19. Apparatus as claimed in claim18 wherein the dust collection means comprises a slidable tray. 20.Apparatus as claimed in claim 18 wherein the dust collection means is insealing engagement with the chamber when the dust collection means is ina closed position.
 21. Apparatus as claimed in claim 3 furthercomprising safety interlock means for preventing firing of the laser ifthe sample presentation means and/or the dust collection means is not ina closed position.
 22. Apparatus as claimed in claim 21 wherein thesafety interlock means comprises electrical interlock means.